The present invention relates to a plunging type constant velocity joint equipped with eight torque transmitting balls, and especially preferably used for a power transmission mechanism for automobile.
There are two types in a constant velocity joint, one of which is a ball fixed type which is able to permit only angular displacement between two axes and the other of which is a plunging type which is able to permit both angular displacement and axial displacement between two axes. They are selectively used, depending on the use conditions, applications, etc. A Zepper type constant velocity joint is representative as the fixed type, and a double offset type constant velocity joint and a tripod type constant velocity joint are representative as the plunging type. As for the plunging type, the tripod type constant velocity joint uses rollers as torque transmitting members, and the others use balls as torque transmitting members.
For example, a double offset type constant velocity joint comprises an outer joint member in which six linear guide grooves are axially formed on an inner cylindrical surface thereof, an inner joint member in which six linear guide grooves are axially formed on an outer spherical surface thereof, six torque transmitting balls disposed in ball tracks formed by cooperation of the guide grooves of the outer joint member and the guide grooves of the inner joint member, and a cage for retaining the torque transmitting balls. Since the spherical center of the outer spherical surface of the cage and the spherical center of the inner spherical surface thereof are offset to the opposite side in the axial direction from the center of pockets, they are called "double offset type". When this kind of joint transmits a torque while taking an operating angle, the cage rotates to the position of the torque transmitting balls moving in the ball tracks in response to the inclination of the inner joint member to retains the torque transmitting balls on the bisector plane bisecting the operating angle. Furthermore, as the outer joint member and the inner joint member relatively displace in the axial direction, a slipping occurs between the outer spherical surface of the cage and the inner cylindrical surface of the outer joint member to ensure a smooth axial displacement (plunging).